A. Severe dysmenorrhea (painful periods) unrelieved by NSAIDs is a hallmark symptom of endometriosis. The condition occurs when endometrial-like tissue grows outside the uterus, leading to inflammation and pain. B. Incorrect → An atypical Papanicolaou (Pap) smear suggests cervical dysplasia, not endometriosis. C. Incorrect → While pelvic inflammatory disease (PID) can cause chronic pelvic pain, it is not directly related to endometriosis. D. Incorrect → Bloating before menses is common in premenstrual syndrome (PMS) and is not a defining feature of endometriosis.